fixing knob on a jacuzzi tub

somehow our cleaning woman broke off the knob on our jacuzzi tub that opens and closes the drain. it looks like it may be a difficult job because the inner workings of the knob are on the inside of the tub. it can only be accessed from a spring-loaded panel on the side of the tub.

has anyone ever had to fix anything on the inside of their jacuzzi tub and how much should this cost?

thanks